JP3061303B2 - Method for producing sintered nickel electrode for alkaline secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a sintered nickel electrode for an alkaline secondary battery by a chemical impregnation method.

[0002]

2. Description of the Related Art As a method for producing a sintered nickel electrode for an alkaline secondary battery, a chemical impregnation method and an electrolytic impregnation method are employed. Fleis
cher, Trans. Electrochem. So
c. 94, 289 (1948);
J. McHenry, Electrochem. Tec
hnol. 5,275 (1967)].

In the chemical impregnation method, a nickel sintered body serving as a substrate is immersed in an aqueous solution of a nickel salt such as nickel nitrate, and the pores of the nickel sintered body are filled with the nickel salt. The nickel salt is immersed in an aqueous alkaline solution to neutralize the nickel salt and convert it to nickel hydroxide, which is an active material. Then, these impregnation steps are repeated until a predetermined amount of nickel hydroxide is completely filled in the nickel sintered body, and thereafter, it is formed in an alkaline aqueous solution, washed with water, and dried to produce a nickel electrode.

[0004] On the other hand, in the electrolytic impregnation method, a nickel sintered body is immersed in an aqueous solution of a nickel salt, then electrolytically reduced, and nickel hydroxide is precipitated in pores of the nickel sintered body. This is a method of manufacturing an electrode, but has a disadvantage that the packing density of nickel hydroxide is lower than that of the chemical impregnation method.

In the impregnation step by the chemical impregnation method, since the impregnating solution is nitric acid acidic, the nickel sintered body is dissolved in the impregnating solution according to the following reaction formula, and 4Ni + HNO ₃ + 6H ₂ O → 4Ni ^{2 +} + NH ₄ ⁺ + 9OH ^-The generated OH ^- causes Ni ²⁺ to precipitate to nickel hydroxide [Ni (OH) ₂ ].

[0006] This phenomenon is remarkable especially in the first impregnation step, and this causes the capacity of the nickel electrode to increase.

The impregnating liquid obtained by the chemical impregnation method contains additives such as zinc salts and cobalt salts in order to improve the utilization rate of the nickel electrode and to suppress the swelling of the electrode due to charge and discharge to improve the cycle characteristics. Is added so that the solid solution eventually becomes a solid solution with nickel hydroxide.

[0008]

However, as described above, the nickel hydroxide formed in the portion where the nickel sintered body is dissolved has a low concentration of additives such as the zinc salt and the cobalt salt. The effect of the additive cannot be fully exhibited.

[0009] For this reason, nickel hydroxide is filled without dissolving the nickel sintered body by dissolving the nickel sintered body by applying an electric potential, but this causes a reduction in the capacity of the nickel electrode. .

The present invention solves the problem that the effect of the additive cannot be sufficiently exerted when the nickel sintered body is melted, and that the capacity is reduced when the melting of the nickel sintered body is suppressed. It is an object of the present invention to provide a sintered nickel electrode having a high capacity and a small swelling due to charge and discharge.

[0011]

According to the present invention, the nickel impregnation is carried out by using an aqueous solution of a zinc salt containing no nickel salt or an aqueous solution of a zinc salt containing no nickel salt and a cobalt salt in the first impregnation. Nickel hydroxide and zinc hydroxide [Zn (OH ₂ ) or zinc hydroxide [Zn (OH) ₂ ] and cobalt hydroxide [C
o (OH) ₂ ] is dissolved, and the effects of these additives can be sufficiently exhibited, thereby achieving the above object.

That is, since the formation of nickel hydroxide by dissolution of the nickel sintered body mainly occurs in the first impregnation step, the first impregnation does not include the zinc salt or the nickel salt containing no nickel salt. By using an aqueous solution of a zinc salt and a cobalt salt, zinc hydroxide, cobalt hydroxide, and the like are dissolved in a necessary concentration in nickel hydroxide produced by dissolution of the nickel sintered body. The effect of the above-mentioned additive can be sufficiently exerted while taking advantage of the increase in capacity due to dissolution of the compound.

Here, the action of the above-mentioned additives such as the zinc salt or the zinc salt and the cobalt salt is described. The additive such as the zinc salt or the zinc salt and the cobalt salt enhances the conductivity of the active material, Further, generation of γ-NiOOH, which causes swelling of the nickel electrode due to charge and discharge, is suppressed.

The swelling of the nickel electrode due to charge / discharge causes a reduction in charge / discharge cycle characteristics. However, the above additive controls the distance between nickel hydroxide crystal layers, and potassium hydrate is formed between the layers. It is considered that the generation of γ-NiOOH is suppressed by making it difficult to penetrate.

In the present invention, examples of the zinc salt include Zn (NO ₃ ) ₂ .6H ₂ O and ZnSO ₄ .7H
₂ O, Zn (CH ₃ COO) ₂ .2H ₂ O and the like are used. As the cobalt salt, for example, Co (NO
_{3) 2 · 6H 2 O,} CoSO 4 · 7H 2 O, Co (CH
₃ COO) ₂ .4H ₂ O or the like is used.

In the first impregnation, an aqueous solution of a zinc salt containing no nickel salt or an aqueous solution of a zinc salt and a cobalt salt not containing a nickel salt is used. % And the concentration of cobalt salt is 1
About 5% by weight is suitable.

For the second and subsequent impregnations, the same impregnation liquid as in the prior art may be used, and a nickel sintered body used as the substrate may be the same as the conventional one.

[0018]

Next, the present invention will be described more specifically with reference to examples.

Example 1 First, a method for producing a nickel sintered body used as a substrate of a sintered nickel electrode will be described. In the following,% indicating the concentration is based on weight.

Nickel powder is added to a gel obtained by mixing 30 g of methylcellulose and 1 liter of water to form a nickel slurry. This nickel slurry is applied to both surfaces of a punching metal (thickness: 70 μm, opening ratio: 25%) made of nickel. The nickel was sintered by heating at 900 ° C. for 20 minutes in a reducing atmosphere to produce a nickel sintered body.

Next, the step of filling the pores of the nickel sintered body with the active material will be described.

First, Co (NO ₃ ) ₂ .6H ₂ O was added to 20
g, 20 g of Zn (NO ₃ ) ₂ .6H ₂ O and HNO
₃ (Nitric acid) was placed in a 2.5 g container, and water was added therein to make the total volume 1 liter, thereby preparing an impregnation liquid to be used for the first impregnation.

The nickel sintered body is immersed in the impregnating liquid for 20 minutes, taken out of the impregnating liquid, dried at 100 ° C. for 30 minutes, and then heated in a 30% aqueous solution of NaOH (sodium hydroxide) heated to 80 ° C. for 10 minutes. Each was converted to hydroxide by immersion. Then, the substrate was washed with pure water until the alkaline component disappeared, and then dried.

Next, Co (NO ₃ ) ₂ .6H ₂ O was added to 5
0 g, 50 g of Zn (NO ₃ ) ₂ .6H ₂ O, Ni (N
The O _{3) 2} · 6H ₂ O to 1000g and HNO ₃ 5 g
The mixture was placed in a container, and water was added thereto to make the total volume 1 liter, thereby preparing an impregnation liquid to be used for the second and subsequent impregnations.

The impregnating liquid used for the second and subsequent impregnations is impregnated with the nickel sintered body under the same conditions as described above.
Neutralize and repeat this impregnation step eight times, then add 30% Na
Amount of nickel hydroxide filled in pores of nickel sintered body (weight increase) with nickel as counter electrode in OH aqueous solution
On the other hand, the battery was charged at 2 C for 60 minutes, discharged at 1.5 C for 45 minutes, washed in pure water until the alkali component disappeared, and then dried to produce a nickel electrode.

Example 2 40 g of Zn (NO ₃ ) ₂ .6H ₂ O and 2.5 g of HNO ₃ were placed in a vessel, and water was added therein to make the total volume 1 liter, which was used for the first impregnation. Prepare the impregnation liquid,
A nickel electrode was manufactured in the same manner as in Example 1 except that this was used for the first impregnation.

Comparative Example 1 In the first impregnation, 50 g of the impregnating liquid [Co (NO ₃ ) ₂ .6H ₂ O used in the second and subsequent impregnations of Example 1;
50 g of Zn (NO ₃ ) ₂ .6H ₂ O, Ni (NO ₃ )
_A nickel electrode was manufactured in the same manner as in Example 1 except that 1000 g of 2.6H ₂ O and 5 g of HNO ₃ were placed in a container, and water was added to make a total volume of 1 liter. .

Comparative Example 2 The procedure of Example 1 was repeated except that the impregnation was carried out using a potentiostat while maintaining the potential of the nickel sintered body in the impregnation liquid at 0.5 V with respect to the Ag / AgCl reference electrode. To produce a nickel electrode. The potential was applied to prevent the sintered body from being dissolved by the impregnating liquid.

Comparative Example 3 The procedure of Comparative Example 1 was repeated except that the impregnation was carried out using a potentiostat while maintaining the potential of the nickel sintered body in the impregnating liquid at 0.5 V with respect to the Ag / AgCl reference electrode. To produce a nickel electrode.

Next, the above Examples 1 and 2 and Comparative Example 1
It used to 3 nickel electrodes as the positive electrode, respectively, a negative electrode using a hydrogen absorbing alloy electrode for a large excess of hydrogen storage alloy having a composition of _{V 22 Ti 16 Zr 16 Ni 39} Cr 7 as an active material, in FIG. 1 The test battery shown was produced.

In FIG. 1, reference numeral 1 denotes a positive electrode, and the positive electrode 1 uses nickel electrodes produced in Examples 1 and 2 and Comparative Examples 1 to 3, respectively. Numeral 2 is a negative electrode, and this negative electrode 2 is made of V ₂₂ Ti ₁₆ Zr ₁₆ Ni as described above.
_It is composed of a hydrogen storage alloy electrode using a hydrogen storage alloy having a composition of ₃₉ Cr _{7 as} an active material.

Reference numeral 3 denotes a separator made of a polypropylene nonwoven fabric, and reference numeral 4 denotes an electrolytic solution. This electrolytic solution 4 is a 30% aqueous potassium solution (however, 17 g / l of lithium hydroxide is added). .

Numerals 5 and 6 denote current collectors made of nickel, and 7 denotes a container made of polypropylene.

The above five types of batteries are charged at 0.1 C for 15 hours, and after charging, the batteries are charged at 0.2 C until the battery voltage becomes 0.9 V.
And the discharge capacity after repeating the charge and discharge twice was examined, and the capacity density was calculated based on the discharge capacity. Table 1 shows the results.

[0035]

[Table 1]

As shown in Table 1, Comparative Examples 2 and 3 in which a potential was applied during impregnation to prevent dissolution of the nickel sintered body were
Although the capacity density was as low as ⁰ mAh · cc ⁻¹ or less, the capacity density of Examples 1-2 and Comparative Example 1 was 450 mAh · cc ^−1.
As described above, the capacity density was about 15% larger than that of Comparative Examples 2 and 3.

Therefore, in Examples 1 and 2 and Comparative Example 1 having large capacity densities, the charge / discharge was continued and the change in the thickness of the nickel electrode due to the charge / discharge was examined. Calculate the degree of swelling of the nickel electrode from the measured thickness of the nickel electrode,
FIG. 2 shows the relationship between the degree of swelling and the number of charge / discharge cycles. In FIG. 2, the initial thickness of each nickel electrode is 10
It is shown at 0%.

As shown in FIG. 2, in Comparative Example 1, the swelling degree was 115% after 50 charge / discharge cycles, but in Example 1, the swelling degree was 107% after 50 charge / discharge cycles.
In Example 2, the degree of swelling was 106 after 50 charge / discharge cycles.
%Met.

When only the swollen portion is compared, the results are shown in Example 1.
In Example 2, the degree of swelling was 45% of Comparative Example 1, Example 2 had a degree of swelling of 40% of Comparative Example 1, and Examples 1 and 2 had lower degrees of swelling than Comparative Example 1.

Since the swelling of the nickel electrode due to the charge / discharge cycle deteriorates the charge / discharge cycle characteristics,
It is expected that the reduction in the degree of swelling as described above will improve the charge / discharge cycle characteristics.

[0041]

As described above, according to the present invention, in the production of a sintered nickel electrode for an alkaline secondary battery by a chemical impregnation method, an aqueous solution of a zinc salt containing no nickel salt is used in the first impregnation. Alternatively, by using an aqueous solution of a zinc salt and a cobalt salt containing no nickel salt, a sintered nickel electrode having a high capacity and less swelling due to charge and discharge could be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a test battery prepared for examining characteristics of nickel electrodes obtained in Examples 1 and 2 and Comparative Examples 1 to 3.

FIG. 2 is a diagram showing the relationship between the number of charge / discharge cycles of the nickel electrode obtained in Examples 1 and 2 and Comparative Example 1 and the degree of swelling of the nickel electrode due to charge / discharge.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Electrolyte

──────────────────────────────────────────────────続 き Continuation of the front page (72) Ryu Nagai 1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell, Ltd. (56) References JP-A-52-97127 (JP, A) JP-A-2 -304867 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4/32 H01M 4/52

Claims (1)

(57) [Claims] 1. A nickel sintered body is immersed in an aqueous solution of a nickel salt, the pores of the nickel sintered body are filled with a nickel salt, and then immersed in an alkaline aqueous solution to neutralize the nickel salt. In producing a sintered nickel electrode for an alkaline secondary battery that repeats impregnation and neutralization to convert to nickel hydroxide, the first impregnation involves an aqueous solution of a zinc salt containing no nickel salt or a zinc salt containing no nickel salt A method for producing a sintered nickel electrode for an alkaline secondary battery, comprising using an aqueous solution of nickel and a cobalt salt.